Ansovino

Using degree-days to manage pests

Insecticides that are applied for a perennial insect pest based only on a calendar date often result in poor insect control and a waste of resources. Phenology models predict timing of events in an organism's development. For many organisms which cannot internally regulate their own temperature, development is dependent on temperatures to which they are exposed in the environment.

Insect activity varies from year to year depending on weather. For example, in Logan, Utah, eggs of the apple pest codling moth began hatching on May 15 in 2005, May 5 in 2006, and April 30 in 2007 – if apple growers always sprayed on May 1, they were not making the most effective insecticide treatment in most years. As long as accurate weather data can be obtained, using degree days to time treatments is more reliable than a calendar date, and allows growers to pinpoint a specific treatment date each year.

Degree days (often referred to as “growing degree days”) are accurate because insects have a predictable development pattern based on heat accumulation. Insects are exothermic (“cold-blooded”) and their body temperature and growth are affected by their surrounding temperature.

Every insect requires a consistent amount of heat accumulation to reach certain life stages, such as egg hatch or adult flight. Degree day values interpret that heat accumulation. When used to determine treatment timing, they are an important component of an Integrated Pest Management program, providing a cost effective tool to reduce insect feeding damage.

Insect-specific data available here may be used in Ansovino's field monitoring and degree-day calculator.

Example: potato tuber moth

Scientific name: Phthorimaea operculella

Location of study: Pukekohe, New Zealand (laboratory studies)

Threshold settings:

• Minimum: 10.0 °C
• Cap: none

Degree-day accumulations required for each stage of development

Source:

• University of California, Division of Agriculture and Natural Resources, Statewide IPM Program
• Foot, M. A. 1979. Bionomics of the potato tuber moth, Phthorimaea operculella (Lepidoptera: Gelechiidae), at Pukekohe. New Zealand Journal of Zoology 6: 623-626.